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Carpal tunnel syndrome, a common and well-described clinical disorder, usually has been considered a chronic disorder with a fixed set of symptoms and typically affecting middle-aged women. Because of the many variations in its initial clinical manifestations, however, its diagnosis at times can be difficult. In this review, we describe nonclassic manifestations of carpal tunnel syndrome and discuss the differential diagnosis, the importance of electrodiag-nostic studies, and treatment modalities.
Although carpal tunnel syndrome is a common and well-described entity, diagnosing this syndrome occasionally can be difficult. Carpal tunnel syndrome usually has been considered a chronic disease with a fixed set of symptoms, affecting women between the ages of 40 and 60 years. It does not, however, always manifest in its well-documented manner. This review describes the various initial manifestations in cases of median nerve compression at the wrist that may be confusing or difficult to diagnose.
Although the disease process was first recognized by Sir James Paget
The carpal tunnel itself is a fibro-osseous structure bounded by eight carpal bones and the flexor retinaculum. Through it pass the median nerve, the nine flexor tendons, and the median artery, when present (Fig. 1). The median nerve then traverses the carpal canal. At its distal end, the median nerve usually divides into its sensory (Fig. 2) and motor branches and many of its autonomic branches.
In the hand, the sensory fibers of the median nerve supply the radial three and a half digits, and the motor fibers usually innervate the abductor pollicis brevis, opponens pollicis, radial half of the flexor pollicis brevis, and the lumbricales to the index and middle fingers. Overlapping innervation of the flexor pollicis brevis by the ulnar nerve is common. Depending on the amount of cross-innervation, movement of the thumb out of the plane of the palm into opposition may be possible by means of muscles innervated by the ulnar nerve. This motion also can occur through anomalous slips of the abductor pollicis longus innervated by the radial nerve.
Thus, the ability to oppose the thumb cannot be interpreted as evidence of function of the median nerve-innervated thenar muscles.
Autonomic fibers carried by the median nerve supply the superficial palmar arch and the digital vessels of the thumb, the index and long fingers, and the radial half of the ring finger through their component digital nerves. These autonomic fibers are responsible for perspiration, and the frequent anhidrosis or hypohidrosis found with median nerve lesions is a result of their dysfunction.
Any process that encroaches on the median nerve within the carpal tunnel, either extrinsically or intrinsically, can lead to the clinical entity of carpal tunnel syndrome. Repetitive motion, overuse, vibration, and direct trauma have been described as possible causes of carpal tunnel syndrome.
When the classic symptoms of numbness or intermittent tingling in the thumb, index and long fingers, and half of the ring finger are found in association with nocturnal pain, thenar atrophy (Fig. 3), weakness of the thumb, positive Tinel's sign over the median nerve at the wrist, and abnormal results of Phalen's test, then carpal tunnel syndrome can easily be diagnosed. It is rare, however, for all these signs and symptoms to coexist in any given case, as demonstrated in a recent study by Stevens and associates.
Data accumulated from medical records from a 20-year period (1961 through 1980) in Rochester, Minnesota, illustrate this point (Table 1). In addition, the lifetime risk of symptoms of carpal tunnel syndrome developing in a specific person was estimated as nearly 10%.
Table 1Symptoms and Signs of Carpal Tunnel Syndrome in 1,016 Patients
Although a combination of the individual classic symptoms is common, patients also can have only one of the cardinal signs, the most common of which is nocturnal pain relieved by shaking the hand. Another variant form is seen in the patient who has had undiagnosed pain in the past and currently has only painless thenar atrophy. Examination usually reveals evidence of sensory abnormality, previously unnoticed by the patient as well. Rarely, a patient may have thenar atrophy and loss of dexterity of the thumb but no pain or sensory disturbance. This manifestation is due to localized entrapment of the recurrent branch of the median nerve at the point of its takeoff from the median nerve.
Older patients sometimes claim that their fingers are “stiff when, in reality, they are numb. More commonly, numbness and stiffness coexist to some extent because patients with arthritis in finger joints also may have joint changes in the wrist that alter the configuration of the carpal tunnel and may predispose to carpal tunnel syndrome. A thorough sensory examination, including evaluation of light touch, two-point discrimination, and, occasionally, measurement of pressure, vibration, or temperature perception thresholds, may disclose the presence of carpal tunnel syndrome.
In contrast, small children do not complain of numb fingers.
Their parents, however, may notice that the index finger and long finger are small or are being excluded from pinching motion or picking up small objects (Fig. 4). These findings also can be diagnostic of a rarer type of carpal tunnel syndrome in which the patient has a long-standing, undiagnosed, complete median compressive neuropathy at the wrist. These correlations should call the attention of the primary-care physician to the problem—that is, a localized median nerve disorder.
Isolated pain in the proximal aspect of the arm or the shoulder on occasion may represent carpal tunnel syndrome.
This pain often occurs at night, and patients may attribute the night pain to poor positioning in bed. More commonly, hand numbness is associated with proximal extension of pain, most often to the proximal part of the forearm but occasionally to the arm, shoulder, or even as far proximally as the ear. Such symptoms usually disappear after carpal tunnel release.
In elderly patients who have carpal tunnel syndrome and proximal shoulder pain at the time of initial examination, the erythrocyte sedimentation rate should be determined. If it is high and they also have morning stiffness, fatigue, low-grade fever, and shoulder or hip-girdle pain, other tests should be performed to establish a diagnosis of polymyalgia rheumatica (up to 15% of patients with this condition have carpal tunnel syndrome
). These patients will respond to corticosteroid therapy. Systemic amyloidosis also must be considered in the differential diagnosis when the erythrocyte sedimentation rate is high.
The combination of neck and wrist pain is a common complaint, especially in patients with osteoarthritis. This pain may be due to compression of the same nerve at two different levels—a “double-crush” lesion.
Less commonly, double compression can involve the median nerve in the forearm and in the carpal canal concurrently. The pronator syndrome is caused by compression of the median nerve in the proximal part of the forearm.
Some patients with pain at the wrist and proximally in the forearm may have such a lesion in addition to carpal tunnel syndrome, but confirmation is difficult because the physical findings may be confused with the more common proximal extension of carpal tunnel pain, and electromyography often is not helpful. If the deep tendinous origin of the pronator teres muscle compresses the anterior interosseous branch of the median nerve, the patient may also have pain in the forearm and weakness or paralysis of muscles served by the anterior interosseous nerve—namely, the flexor pollicis longus, the flexor digitorum profundus of the index and middle fingers, and the pronator quadratus. Distinguishing a single lesion from a double lesion is important for effective treatment of the patient.
Numbness of all five fingers rather than just the radial three and a half digits can be due to concomitant entrapment of the median nerve at the carpal tunnel and the ulnar nerve either at the elbow or, more rarely, at the wrist. In the former instance, the patient would have numbness on the dorsoulnar aspect of the hand in addition to numbness of all fingers. Ulnar nerve symptoms, however, can also be produced by compressing or stretching the ulnar nerve if the patient leans on the flexed elbows while Phalen's test is performed.
Raynaud's phenomenon, reflex sympathetic dystrophy, and diabetic neuropathy all must be considered in the differential diagnosis, but these diseases may coexist with carpal tunnel syndrome. In Raynaud's phenomenon, symptoms that are most severe in the distribution of the median nerve can be seen in association with carpal tunnel syndrome. Carpal tunnel syndrome may coexist with reflex sympathetic dystrophy, either as the primary cause of the abnormal autonomic reflex arc or secondary to the hand swelling that is so common in established cases. In diabetes,
nerves are more sensitive to compression. Isolated or multiple entrapments of peripheral nerves at fibro-osseous regions can occur. One must determine whether a mechanical lesion is indeed present, distinct from or superimposed on a generalized neuropathy.
Numbness associated with fullness of the soft tissues at the wrist suggests the presence of a tenosynovitis that may be idiopathic or due to work hypertrophy, trauma, an endocrine disorder (for example, hypothyroidism or acromegaly), pregnancy, or an inflammatory process (such as rheumatoid arthritis, septic tenosynovitis, or, more rarely, mycobacterial or fungal tenosynovitis). These patients have swelling in the distal aspect of the forearm and stiffness in the fingers as well as more characteristic symptoms of carpal tunnel syndrome.
The association of carpal tunnel syndrome with trigger finger, de Quervain's tenosynovitis, or basal joint arthritis of the thumb is significant. Up to 25% of patients who require operation for pantrapezial arthritis will require release of the carpal tunnel as well.
A patient who is on long-term renal dialysis and has an arteriovenous shunt in the forearm is vulnerable to carpal tunnel syndrome in the same arm. The increased vascularity, venous hypertension, and associated edema have been proposed as possible mechanisms for the resultant nerve compression. Recently, amyloid deposits consisting of β2-microglobulin have been isolated in the flexor synovium of patients with dialysis-associated carpal tunnel syndrome.
The exact relationship between localized or systemic amyloidosis and carpal tunnel syndrome has not yet been well established.
A patient with a fusiform soft-tissue mass in the palm or distal part of the forearm may have the numbness typical of carpal tunnel syndrome. During movement the mass tenses, and on flexion the mass moves proximally. This mass can be a hypertrophied lumbrical muscle,
an enlarged flexor digitorum superficialis extending from the forearm into the hand, an anomalous muscle, or flexor tenosynovitis as described.
A patient with injury to the flexor tendons in a digit can also have carpal tunnel syndrome. Such a patient may have numbness in the distribution of the median nerve in the hand and inability to flex the fingers as a result of tendon rupture after a sports injury or in rheumatic disease. The carpal tunnel symptoms are due to the proximal migration of the lacerated or ruptured tendon encroaching on the carpal canal.
can extend to involve the entire width of the palm. Low density on a roentgenogram is the key to diagnosis. It can manifest, with or without carpal tunnel syndrome, as a large mass distal to the carpal canal.
Lipofibroma of the median nerve (Fig. 5), a benign tumor of nerve, manifests as a fusiform swelling that usually extends proximally to the wrist flexion crease.
This tumor can appear as a mass alone, in association with digital gigantism, or with numbness and atrophy. The extent of carpal tunnel compression depends on the size of the hamartomatous mass and the extent of its compression of normal nerve fibers.
recently was described in patients who had pain in the wrist or numbness in the radial three and a half digits, or both, directly related to manual labor and relieved by rest. These patients typically have no symptoms, and results of physical examination and electrical studies with the patient at rest are normal. Provocative stress testing with work stimulators may reproduce the symptoms of carpal tunnel syndrome and also produce swelling in the affected hands, as confirmed by a substantial increase in volume and diminished monofilament sensibility.
In all the cases discussed thus far, the symptoms of carpal tunnel syndrome are gradual in onset, occurring during a period of months or years. An acute carpal tunnel syndrome also can occur.
The most common cause is major trauma such as fracture or dislocation of the wrist, but some patients who have suffered a relatively minor trauma may be afflicted with acute and unremitting symptoms of carpal tunnel syndrome within minutes or hours after the injury, especially in patients with bleeding dyscrasias who have acute hemorrhage into the carpal canal.
Persistent and recurrent carpal tunnel syndromes are possible. In approximately 5% of cases of surgically treated carpal tunnel syndrome, the patient has no response or worsening after the surgical release. In a similar percentage, symptoms may redevelop at the same site. These events can be due to inadequate release, advanced pathologic changes in the nerve, mechanical changes in the distal carpal row postoperatively, or a fibroblastic response.
It is far more common, however, for carpal tunnel syndrome to develop in the opposite extremity (30%) or for some other entrapment complex or generalized peripheral neuropathy to develop in either arm.
Many conditions can mimic the carpal tunnel syndrome. Awareness of the differential diagnosis is critical in making the proper diagnosis.
The history and physical examination often rule out sites away from the wrist as being responsible for the symptoms. A complete review of symptoms should be done because carpal tunnel syndrome often is associated with other diseases (Table 2). Treatment of the systemic disease may resolve the symptoms of carpal tunnel syndrome.
Table 2Selected Conditions Associated With Carpal Tunnel Syndrome
Acute or chronic trauma to forearm, wrist, or hand
Cervical radiculopathy generally can be excluded if the hand symptoms are not provoked by passive stretching of the neck into extension and by lateral flexion toward the side of the affected hand. Extension of the pain to the chest or posterior scapular region would help confirm neck involvement either as an isolated condition or, when combined with specific signs and symptoms at the wrist, as part of a double-crush syndrome. Electromyographic studies are especially helpful in such cases; fibrillation in the paravertebral muscles or F-wave abnormalities would confirm neck involvement, whereas localized conduction delay at the wrist would confirm carpal tunnel syndrome. Other more proximal neuropathies that can be confused with carpal tunnel syndrome include thoracic outlet syndrome, idiopathic brachial plexitis (Parsonage-Turner syndrome), and nerve entrapments in the forearm—namely, the pronator and anterior interosseous nerve syndromes discussed in the foregoing material.
In generalized neuropathy, in addition to common medical conditions such as diabetes mellitus, the possibility of a drug history or chemical or industrial exposure should be carefully explored. Both nutritional deficiencies and vitamin toxicity may cause general neuropathies. Other peripheral extremity involvement also is important in considering this particular diagnosis. Clinical or electrical evidence of multiple neurologic problems in the extremities suggests a generalized neuropathy.
Central nervous system involvement, such as focal motor seizures, transient ischemic attacks, or migraine headaches, usually manifests itself in the hands with symptoms of clumsiness or slowness of movement rather than painful paresthesias. A sensory stroke or a syringomyelia must also be considered. Vascular disorders, especially Raynaud's phenomenon, often involve the fingers equally; the physician should note whether the patient has systemic manifestations that might be suggestive of scleroderma or other collagen disorders. In reflex sympathetic dystrophy, swelling of the entire hand and fingers is common, but electromyographic studies will determine whether the swelling is associated with neural compression. Reflex sympathetic dystrophy can be confirmed by triple-phase technetium bone scans or specific studies of autonomic function. Again, one must keep in mind that some patients with Raynaud's phenomenon or reflex sympathetic dystrophy also have carpal tunnel syndrome.
If both median and ulnar nerves are involved, one must rule out a median cord lesion such as could be caused by a Pancoast tumor or a neoplasm such as a neurilemoma involving the brachial plexus. Chest roentgenography (apical view), electromyography, and magnetic resonance imaging may be necessary.
Electrodiagnostic studies have proved to be invaluable in confirming the diagnosis of nerve entrapments and in establishing the specific location.
In addition, they help identify other neuromuscular disorders that can coexist or may be underlying. Investigators have identified a subclinical variant of carpal tunnel syndrome with electrical abnormalities but no clinical manifestations. Patients with these findings may be at increased risk for development of overt symptoms of carpal tunnel syndrome in the future.
The most sensitive electrodiagnostic manifestation of carpal tunnel syndrome is an abnormality, either in latency (conduction time) or in amplitude of the transmitted signal, of sensory conduction across the wrist. These findings usually can be correlated with nerve fiber pathologic findings. As axons become avascular or demyelinated, both the conduction and the amplitude of the electrical response change. If demyelination occurs, serial studies will help recognize the developing process. Finer segmental studies such as digit-to-palm and palm-to-wrist conduction studies with comparison of the thumb, index finger, and long finger can yield a 95% correlation with a clinical diagnosis of carpal tunnel syndrome. Patients with characteristic clinical findings of carpal tunnel syndrome, however, can have normal nerve conduction because of technical factors or because of involvement of only a relatively small percentage of axons in the pathologic process.
Other abnormalities include motor conduction delay and fibrillation or positive sharp waves in the thenar muscles on electromyography.
Signs of poor prognosis include considerably prolonged conduction (2 to 3 times normal) and absence of sensory or motor conduction. Similarly, fibrillations with atrophy usually are seen on electromyography in patients with advanced compression. An even worse sign is absence of fibrillations and fibrotic thenar muscles as determined by needle insertion.
For the classic manifestation of carpal tunnel syndrome and many of the variant types, initial treatment is conservative. The wrist may be splinted in neutral position full-time for 3 weeks and then only at night for 3 more weeks. Injection of corticosteroids into the flexor tenosynovium under the flexor retinaculum may diminish the inflammation and relieve the symptoms.
It is important not to inject the median nerve itself; if paresthesias are elicited on insertion of the needle, the needle should be withdrawn and reinserted. Up to three or four injections are reasonable if separated in time. Nonsteroidal anti-inflammatory drugs and diuretics also may be prescribed.
The use of pyridoxine to treat carpal tunnel syndrome is controversial, particularly because pyridoxine abuse itself may cause a neuropathy.
None of the nonoperative managements of carpal tunnel syndrome has been studied scientifically in comparison with untreated control cases. In a recent survey of the members of the American Society for Surgery of the Hand,
the regimen of splinting and corticosteroid injection was the one used most widely. Between a half and three-quarters of all patients who are diagnosed clinically as having carpal tunnel syndrome have relief of symptoms without surgical treatment.
An operation is indicated when conservative therapy yields no response, symptoms are severe, and, especially, the patient has clear-cut abnormalities on electrodiagnostic tests, thenar atrophy, or a measurable decrease in sensibility in the median nerve distribution. These findings all indicate ongoing axonal injury. Some investigators recommend immediate carpal tunnel release for acute posttraumatic carpal tunnel syndrome.
Pregnant women who have carpal tunnel syndrome should not undergo surgical treatment during pregnancy unless the symptoms are disabling; such symptoms often disappear after delivery. Of the patients who are treated surgically, 90 to 95% experience some improvement in sensory and motor function.
The surgical treatment of carpal tunnel syndrome consists of complete release of the flexor retinaculum. The most common cause of “recurrence” actually is incomplete release of the retinaculum. Surgical exposure should be generous enough to allow release under direct vision. “Blind” division of the retinaculum through a small incision may result in iatrogenic injury to the nerve, particularly the motor branch. Adjunctive procedures, such as neurolysis and retinacular reconstruction, are controversial and probably add little to the benefit of carpal tunnel release for most patients. Such procedures, however, are indicated in selected cases in which severe scarring or tendon subluxation out of the released carpal tunnel is present.
One study reported that 85% of patients with thenar atrophy who have undergone neurolysis that included the recurrent branch will gain opposition of the thumb.
In some patients, however, this ability may represent ulnar or radial nerve function rather than median nerve recovery. In the occasional case in which thenar atrophy has progressed to fibrosis and the patient is unable to oppose with ulnaror radial-innervated muscles, opposition tendon transfer may also be performed at the time of decompression.
When carpal tunnel syndrome is associated with the cumulative trauma of work stress, avoidance of repetitive motions and extreme wrist positions is important. If followed by a return to the same traumatic environment, operation is often unsuccessful in controlling symptoms in such patients. Patients with dynamic carpal tunnel syndrome usually respond well to a modification of work activity, such as decreasing the speed, resistance, or hours involved in repetitive work. In refractory cases, surgical treatment may be necessary.
We thank Dr. Robert C. Bahn for his careful reading of the submitted manuscript and beneficial suggestions.
Lectures on Surgical Pathology. Lindsay & Blakiston,